The present invention relates to an arrangement for opening and closing coverings for architectural openings such as Venetian blinds, pleated shades, cellular shades, and vertical blinds.
Usually, a transport system for a covering that extends and retracts in the vertical direction has a fixed head rail which both supports the covering and hides the mechanisms used to raise and lower or extend and retract the covering. Such a transport system is described in U.S. Pat. No. 6,536,503, Modular Transport System for Coverings for Architectural Openings, which is hereby incorporated herein by reference. In the typical covering product that retracts at the top and then extends by moving downwardly from the top (top/down), the extension and retraction of the covering is done by lift cords suspended from the head rail and attached to the bottom rail. In a Venetian blind, there also are ladder tapes that support the slats, and the lift cords usually run through holes in the middle of the slats. In these types of coverings, the force required to raise the covering is at a minimum when the covering is fully lowered (fully extended), since the weight of the slats is supported by the ladder tapes, so that only the bottom rail is being raised by the lift cords at the outset. As the covering is raised further, the slats stack up onto the bottom rail, transferring the weight of the covering from the ladder tapes to the lift cords, so progressively greater lifting force is required to raise the covering as it approaches the fully raised (fully retracted) position.
Some window covering products are built to operate in the reverse (bottom-up), where the moving rail, instead of being at the bottom of the window covering bundle, is at the top of the window covering bundle, between the bundle and the head rail, such that the bundle is normally accumulated at the bottom of the window when the covering is retracted and the moving rail is at the top of the window covering, next to the head rail, when the covering is extended. There are also composite products which are able to do both, to go top-down and/or bottom-up. In the top-down/bottom-up (TDBU) arrangements, the window shades or blinds have an intermediate movable rail and a bottom movable rail.
Known cord drives have some drawbacks. For instance, the cords in a cord drive may be hard to reach when the cord is high up (and the blind is in the fully lowered position), or the cord may drag on the floor when the blind is in the fully raised position. The cord drive also may be difficult to use, requiring a large amount of force to be applied by the operator, or requiring complicated changes in direction in order to perform various functions such as locking or unlocking the drive cord. There also may be problems with overwrapping of the cord onto the drive spool, and many of the mechanisms for solving the problem of overwrapping require the cord to be placed onto the drive spool at a single location, which prevents the drive spool from being able to be tapered to provide a mechanical advantage.
It often is desirable to hide the cords so there are no loose cords. However, this can be difficult, especially when there is more than one movable rail, which generally means that there are many cords that have to be hidden.